Recently, the electrical wiring device industry has begun to substitute lightweight inexpensive materials such as molded plastic for metal parts, including the mounting straps in such devices. Traditionally, electrical wiring devices have been mounted to an electrical outlet box by means of a flat head screw which is beveled along the bottom of the screw head. The device mounting screws which extend through apertures in the mounting strap are often driven by a power tool (as well as by hand) into an appropriate opening in the electrical outlet box.
This conventional mounting screw arrangement has worked satisfactorily with devices having metal mounting straps. However, when non-metallic materials have been substituted for metal straps, in the form of plastic integral mounting straps, a problem has developed when the conventional mounting screws are installed. The power tool operator (or installer) does not know exactly when the screw is fully turned down and therefore when to stop. This often results in the screw cutting into the plastic of the integral mounting strap and greatly weakening the area of securement. Sometimes the screw can even "chew" through the material surrounding the mounting aperture on the strap, thus rendering ineffective the mounting at that end. (For metal screws used with metal straps, this is not a significant concern because the metal strap can easily withstand the frictional forces generated by the turning screw).
Accordingly, there is a need for a new and improved mounting screw which avoids the foregoing disadvantages. It is therefore an object of the present invention to provide a new and improved mounting screw for use with non-metallic mounting straps.
It is also an object of the invention to provide such a screw which will resist damaging the non-metallic mounting strap.
It is a further object of the invention to provide such a screw which resists further turning when its screw head has been fully turned, thus signaling the power tool operator (or installer) to stop turning so as to prevent the screw from cutting through the aperture in the non-metallic integral mounting strap.
It is a further object of this invention to provide a new and improved mounting screw which is compatible with all non-metallic materials.
It is an additional object of the invention to provide a combination electrical wiring device with non-metallic mounting straps and mounting screw wherein there is little or no danger of weakening the area of securement on the mounting strap if the screw is overturned. Such a combination overcomes the present problems because the mounting screw resists further turning when its screw head has been fully turned signaling the power tool operator (or installer) to stop turning.